1. Field of the Invention:
The present invention relates to a method for manufacturing a thick asphalt sheet which includes preparing a thick sheet material made of non-woven fabric of synthetic fibers and impregnating said sheet material from its both sides with a molten petroleum asphalt material or molten petroleum asphalt materials of different kinds, respectively, to form a thick asphalt sheet.
The present invention further relates to a method for making a waterproofing surface by using the thick asphalt sheet thus manufactured.
2. Description of the Prior Art:
Heretofore, an asphalt sheet, usually called as an asphalt roofing, which is one of waterproofing materials, has been manufactured by firstly preparing a sheet material made of waste cotton pieces, staple fibers of synthetic material or the like and impregnating said sheet material with molten asphalt material. The asphalt roofing heretofore manufactured has a thickness of about 1 mm and, consequently, it has a relatively low strength against tension. Accordingly, if such asphalt roofing is used to cover a concrete ground, it cannot follow a crack which may be produced on the surface of the concrete ground, so that the asphalt roofing becomes cracked. In order to form a crackless waterproofing layer on a concrete ground, it was heretofore required to put two or more layers of the asphalt roofing on the concrete ground. Such construction of two or more asphalt roofing layers requires complicated operations and, during the period where the weather is changeable, the waterproofing work requires relatively long period, and the construction work may be delayed.
In order to eliminate such disadvantages of the prior art owing to defects of material or complicated work as required, a new asphalt sheet was recently developed. This newly developed asphalt sheet is manufactured by preparing a sheet material having a thickness of about 6 mm made of endless and long fibers of synthetic material by so-called needle punching process, using paste material, and impregnating said sheet material with molten petroleum asphalt. The new asphalt sheet has a thickness three to four times as much as that of the conventional asphalt sheet and it is formed by a sheet material made of long and endless fibers which are entangled together into an integral body. Accordingly, it has a high strength against tension and a capability of following a relatively large crack which may be produced in a surface of a concrete ground. Thus, the above newly developed asphalt sheet is expected to be an asphalt roofing which provides a perfect waterproofing property and which can attain its object only by applying one layer of the asphalt sheet.
The newly developed asphalt sheet, however, has a disadvantage in that it is very difficult to completely impregnate the thick sheet material of non-woven fabric with molten asphalt material having high viscosity.
Upon the extensive study, we developed various methods of impregnating the thick sheet material of non-woven fabric with molten asphalt material. One of these methods employs rolls having needle-like projections thereon to form apertures in the sheet material, so that the molten asphalt material can pass into the central portion of the sheet material through the apertures formed in the sheet material. The other method employs an asphalt melting tank having great depth, in which the molten asphalt material can pass into the central portion of the sheet material under the action of hydraulic pressure difference and temperature difference.
These methods, however, have such disadvantages that the processing speed is low, so that it is difficult to attain a desired production efficiency, and the equipment used is of large-scale, owing to inclusion of the asphalt melting tank in any case.